What kind of spiders shed their skin

Exoskeleton segments are connected together with joints so the spider can move them back and forth. Muscles attached on the inside of the exoskeleton contract to move the legs inward, but spiders don't have any muscles to extend the legs back out again. Instead, they have to force bodily fluids mainly blood into the legs to push them outward. If a spider loses too much body water, it can't generate the necessary hydraulic pressure to push its legs out.

This is why you sometimes see spiders on their backs with their legs curled up. The exoskeleton is made of several layers of cuticle , a composite material containing various proteins and chitin , a long-chain polysaccharide sugar. The chitin and protein molecules are arranged in long chains, in successive layers, like the grain in plywood.

This structure makes cuticle extremely strong, as well as highly effective at keeping the spider from drying out, but the material does have one serious drawback. While it's flexible enough for movement, it can't expand like human bones and tissue -- in other words, it can't grow. In order to increase its size, the spider has to form a new, larger cuticle exoskeleton and shed its old one this is called molting.

The first outward sign that a snake is ready to shed is that its eyes turn a milky color. Patches of mucus between the lower and upper layers of skin begin to appear.

As the mucus increases, the layers disconnect and eventually the old layer splits, usually at the top of the head, then down the back.

Shedding skin not only frees up room, for some geckos and anoles, it's also a snack, Vitt says. Notably, snakes will not eat their old skin. Have a question about the weird and wild world? Tweet me , leave me a note in the comments, or find me on Facebook. Weird Animal Question of the Week answers your questions every Saturday. All rights reserved. Lift Off Growing larger causes spiders to molt, a process called ecdysis, Jo-Anne Sewlal , an arachnologist at the University of the West Indies, says via email.

Share Tweet Email. Read This Next Wild parakeets have taken a liking to London. Animals Wild Cities Wild parakeets have taken a liking to London Love them or hate them, there's no denying their growing numbers have added an explosion of color to the city's streets. India bets its energy future on solar—in ways both small and big. This new, folded exoskeleton is ready to expand as soon as the old one is shed. The spider takes in air and uses the concentrated pressure of its blood to enlarge its body, cracking the old exoskeleton.

Next, the spider pushes itself out through this fissure. The soft, unprotected spider now takes in air to create even more room in the soft exoskeleton, allowing for additional growth. The new exoskeleton then begins to harden, and when it reaches the proper degree of firmness, the molting process is complete. Molting can be quite a dangerous process for the spider. Most molts take quite a bit of time to complete. Moreover, without their protective exoskeleton, spiders are very vulnerable to attack by predators.

During and immediately after they shed their old skin, their only protection is their new, soft exoskeleton. According to Cornell University, approximately 85 percent of arthropod deaths occur during the molting phase.

Some spiders may even experience difficulty extracting themselves from their old exoskeletons. The result can be mutilation or a form of suffocation. To protect themselves during molting, some spiders hide. The spiders gain weight by eating insects.

If they capture fewer insects, then they should take longer to gain enough weight to molt. I tested this prediction by collecting adult female spiders from a Texas population Brazos Bend State Park and letting them lay in the laboratory.

I reared their offspring to the fourth instar, then randomly assigned 10 spiders to one of five different diets, determined as a proportion of their initial body mass: 2. As the amount of food they ate increased, the rate at which the spiders gained weight also increased and the number of days they spent in the fourth instar declined, supporting my hypothesis Higgins and Rankin It appears that spiders have no effective manner of detecting that they have eaten enough, and overeating is a mortal risk.

It happens in the wild, also: one spider I tracked over several days in Panama had spun her web in what appeared to be a prime location beside a bee nest. She always had large numbers of bees in her web and was eating when ever I checked on her, but she died the next time she attempted to molt. An alternative explanation is that these high diets are somehow nutritionally unbalanced, but then why would spiders getting low and moderate amounts to eat do just fine even when it took them a month to get large enough to molt?

What determines how much a spider grows when it molts? This is basically the same as the question "how much new exoskeleton fits inside the old one? Their abdomen expands as they gain weight the exoskeleton is stretchy , but the size of the legs and cephalothorax are fixed, and only change when they molt.

The arrow-heads in this figure from my publication show the average size of mature females in each of these three populations. There are two arrow heads for Panama, because that population produces two generations each year and they mature at different sizes. When ever I study new populations, I always collect these data. Comparing the slopes of the lines - the slope being the growth at each molt - I have discovered that the amount of growth per molt is fixed invariable within a population, and varies little among populations.

Even the giant N.